A driver which moves a driving tool and drives a fastener into a material to be driven by utilizing the restoring force of an elastic body such as a coil spring is known. Some of drivers of this type are provided with a mechanism for absorbing or reducing the reaction caused when the fastener is driven.
For example, Patent Document 1 describes a weight (weight device) which is moved in the opposite direction of a driving direction to reduce the reaction at the driving when an active member (active device) provided with a nail driving tool is moved in the driving direction of a nail. A rack gear is formed on each of the active member and the weight. Moreover, a common pinion gear always meshed with each rack gear is provided between the active member and the weight. Along with the rotation of the pinion gear in a predetermined direction, the active member is moved in the direction opposite to the driving direction, and the weight is moved in the driving direction. Then, when the active member is moved in the driving direction while rotating the pinion gear in the direction opposite to the above-described predetermined direction, the weight is moved in the direction opposite to the driving direction along with the rotation of the pinion gear, so that the reaction at the driving is reduced.